An annual service is the cheapest insurance a boiler owner has, but the word 'service' covers a wide range of actual work, from a five-minute visual check to a full case-off inspection with combustion analysis.
This guide sets out what should happen during a proper service, what that tends to cost, and where the price moves for landlords, oil boilers and larger system boilers.
What a proper service includes
- Visual inspection of the boiler casing, seals and flue for damage or corrosion
- Case off, checking the burner, heat exchanger and internal components
- Combustion analysis, checking the flue gas readings against manufacturer tolerances
- Checking the condensate trap and pipe for blockages
- Checking system pressure, expansion vessel charge and safety devices
- A written record for the manufacturer warranty and, where relevant, the landlord's file
Indicative price bands
| Service type | Indicative range | Notes |
|---|---|---|
| Combi boiler service | £70 to £100 | Most common domestic job |
| System or regular boiler service | £80 to £110 | Extra time on cylinder-linked controls |
| Oil boiler service | £90 to £130 | Nozzle, filter and fuel line checks add time |
| Landlord gas safety certificate (CP12) combined with a service | £100 to £150 | Two jobs done in one visit |
Gas versus oil, why oil costs more
Oil boilers need the fuel line, filter and nozzle checked and often replaced as part of a service, and the burner is set up to a specific fire rating using a smoke and CO2 test. That extra component work is why oil servicing tends to sit above gas servicing.
Why a landlord combines a service with a CP12
A landlord gas safety certificate only confirms the appliances are safe on the day of the check. It is a different, legally required inspection from a service, which is about keeping the boiler running efficiently and under warranty.
Doing both in one visit means the engineer is already on site with the case off, so it is usually cheaper than booking them separately, and it means one appointment for the tenant rather than two.
Why a cheap 'service' is sometimes just a look
Some very low-cost service call-outs are, in practice, a visual check and a pressure test without the case coming off. That is not a fault of the engineer, it is simply a shorter job, and it will not catch a cracked heat exchanger or a flue gas reading drifting out of tolerance.
If a service price looks unusually low compared with others, it is worth asking directly whether the case is removed and whether a combustion analyser reading is taken and recorded.
Timing it before the switch-on
Booking a service in late summer or early autumn, before the heating goes back on for the season, means any fault is caught while the boiler is not under daily demand, and before engineers are at their busiest with breakdown call-outs in the first cold snap.
What a proper record actually captures
A service is only worth the paper it is written on if the paperwork actually says something. A proper record should note the flue gas readings taken with a calibrated combustion analyser, the boiler's operating pressure before and after any adjustment, the condition of the condensate trap, and confirmation that the flame picture and burner were checked with the case off.
It should also list the boiler's model and serial number, the date, and the engineer's Gas Safe licence number, since these are the details a manufacturer or insurer will ask for if a claim ever needs supporting.
- Combustion analyser reading, compared against the manufacturer's stated tolerance
- Operating pressure and any top-up carried out
- Condensate trap and pipe condition
- Flue and terminal condition, including clearance checks
- Safety device checks, such as the flame supervision device
- Engineer's Gas Safe number and the boiler's serial number
What can invalidate a warranty
Most manufacturer warranties are conditional on an annual service being carried out by a Gas Safe registered engineer and, in many cases, on the boiler having been commissioned with a manufacturer-approved filter and correctly dosed inhibitor at installation. Missing even one annual service, or having it done outside the window the manufacturer allows, can be grounds for a warranty claim to be refused.
Using an unregistered installer for any work on the appliance, fitting non-approved parts, or failing to register the warranty within the manufacturer's stated period after installation are the other common ways a warranty is lost. Keeping every service record together, including the one from the year of installation, is the simplest way to avoid a dispute later.
Frequently asked questions
- How do I know if my service included a case-off inspection?
- Ask for the combustion analysis reading. If a figure was recorded and compared with the manufacturer's tolerance, the case was almost certainly off.
- Do combi and system boilers cost the same to service?
- They are close, but system boilers linked to a cylinder and additional controls can take slightly longer, which is sometimes reflected in the price.
- Can I get a service and gas safety certificate in one visit?
- Yes, this is common for landlords and is usually cheaper than booking the two separately since the engineer is already on site.
- What happens if a fault is found during a service?
- You'll be told what was found and given a separate quote for the repair. A service itself does not usually include remedial parts or repair labour.
Book your annual service before autumn
A proper case-off service, with a written record for your warranty or landlord file.